Laser printers use a coherent beam of light, hence the term “laser printer,” to expose discrete portions of an image transfer drum thus attracting the printing toner. Toner is a mixture of pigment (most commonly black) and plastic particles. The toner becomes electrostatically attracted to exposed portions of the image transfer drum. The toner is transferred to paper, or other medium, as it passes over the rotating image transfer drum. Subsequently, the paper is heated so that the plastic is melted thereby permanently affixing the ink to the paper.
The vast majority of commercially available desktop laser printers include replaceable or removable toner cartridges that incorporate an image transfer drum, a toner tank, and a metering system. A drive mechanism is connected to the drum and metering system. Modern toner cartridges often include a variety of sensors that interact with the laser printer to indicate the status of the cartridge. Indications relating to toner level, print quality and general cartridge function are often included as well. A large number of types and sizes of toner cartridges are currently available. The sensing system typically includes an encoder wheel interconnected with a rotating agitator within a cylindrical toner tank. Movement of the agitator feeds toner into the metering system. The encoder wheel reports the movement of the agitator through the toner reservoir.
A particular failure of the devices of the prior art is the use of a yieldable drive assembly in the agitating mechanism. Such agitating mechanisms require low profiles to minimize drag as they move through the toner so that the agitator can spring forward as soon as the end of the agitating mechanism exits the toner. The resulting low profile agitating mechanisms don't optimize agitation of the toner.
Furthermore, the torque exerted upon a yieldable drive apparatus is concentrated on the outer tip of the yieldable drive shaft. Furthermore, impulse forces can shear the tip of the shaft where the range-of-motion limiting device is connected when the yieldable drive paddle contacts toner that has become packed (during non-use).